The present invention relates in general to the art of earth boring and more particularly to a chuck for clampingly engaging an element of a rotary drill string or the like. Earth boring machines that drill by the rotary method utilize a drill string with a drill bit attached at the lower end. The drill string is rotated and forced downward causing the bit to penetrate into the earth. The earth boring machine that supplies the rotary and axial forces must have a chuck means for clampingly engaging the drill string. Difficulties have been encountered with prior art drilling machines with respect to the chuck means for clampingly engaging the drill string and applying the rotary and axial forces. The present invention provides an improved chuck apparatus for clampingly engaging the drill string. A multiplicity of jaws are provided positioned at intervals around the drill string thus improving their gripping ability and reducing the danger of damaging the drill string. The jaws may be easily removed from the earth boring machine and new jaws inserted in their place. This allows worn jaws to be replaced or sets of jaws for different size drill strings to be used in the same earth boring machine. A cover is removed and the jaws are simply withdrawn. The jaws are all connected together as a set which facilitates removal of the jaws and insures that the jaws will be retained together as a set during transit and storage. Means are provided for containing the jaw actuating spring pressure during removal of the jaws. Indicator means are connected to the jaw actuating means for indicating the position of the jaw actuating means.